Field of the Invention
The present invention relates to the field of thrusters for marine vessels, such as power boats and sailboats, typically used as leisure craft. More particularly, it relates to thrusters that are able to move between a deployed position when in use, and a retracted position when not in use. In the art, these thrusters have previously been known as ‘swing’ thrusters, but are more properly referred to as retractable thrusters.
Related Art
It is known that addition of thrusters to marine vessels improves their manoeuvrability. This is of particular advantage when, for example, manoeuvring within a port or harbour, where space is often limited, and manoeuvring takes place at low speed.
Thrusters use a pair of cooperating propellers, driven by an electric or hydraulic motor, in order to provide a thrust of water in the required lateral direction.
Various types of thruster are known in the art already. Bow thrusters are used to control lateral movement of the bow. One type of bow thruster is a tunnel thruster, in which a tunnel is installed laterally through the bow region of the hull. Tunnel thrusters are generally used for larger vessels. The tunnel is installed in the hull below the waterline. This takes up a large amount of internal space and so this approach is not considered suitable for smaller vessels where hull space is often limited.
For smaller vessels, or for vessels having a hull designed for planing, in which the bow part of the hull may have a very shallow draft, an alternative approach lies in a retractable thruster. A retractable thruster is held within the hull when not in use, in a storage configuration, in order to avoid effects of drag. The retractable thruster is extended outboard from the hull when needed, in a deployment configuration. It is in view of the type of motion employed to deploy the thruster that some such thrusters have previously been referred to as ‘swing’ thrusters.
Known retractable thrusters have the propellers located in a tunnel, the propellers being mounted on a common shaft in the tunnel, the common shaft being connected by a drive shaft to a motor (typically electric but optionally hydraulic) and a deployment mechanism for moving the tunnel with its associated propellers and the drive shaft between the storage and deployment configurations. Typically, the deployment mechanism includes an actuator.
EP-B-1512623 discloses a steering device comprising a propeller unit attached at a first end of a main carrying arm, and a motor attached at a second end of the main carrying arm. The main carrying arm is arranged to pivot through a recess in a rigid housing. In operation, therefore, both the motor and the propeller unit rotate between the storage and deployment configurations. In order to accommodate this movement, a flexible sealing ring is provided between the main carrying arm and the housing.
EP-B-2548797 discloses a retractable thruster comprising a propeller unit arranged for moving along an arc about a first centre of rotation between a retracted and an extended position. A door is attached to the propeller unit. The door is arranged to be rotated about a second centre of rotation opposite to that of the rotation of the propeller unit. EP-B-2548797 also provides a motor which is fixed in an upright position relative to the hull of the vessel. The drive shaft linking the motor and propeller unit has a foldable double cardan joint in order to accommodate the movement of the propeller unit relative to the motor.